Scientists Monitor Killer Mice … From Space

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NASA satellites hovering hundreds of kilometers above the Earth
may now be able to track a very terrestrial threat: mice.

According to a new study published Wednesday (Feb. 16) in the
journal Global Ecology and Biogeography, satellite images showing
changes in vegetation (food for mice) can be used to predict the
risk of mouse-borne disease outbreaks. Flourishing vegetation
generally means a mouse baby boom, and that, in turn, means
more rodents carrying hantavirus, a respiratory disease that
can be fatal when spread to humans.

The method "potentially could be applied to any animal that
responds to vegetation," study co-author Denise Dearing, a
biologist at the University of Utah, said in a statement. "It
would have to be calibrated against each specific species of
rodent and the disease, but it's really powerful when it's done."

Hantavirus is an ailment spread when people
inhale dust containing mouse feces or urine. Only 503 human
cases of hantavirus were reported between 1993 and 2009,
according to the Centers for Disease Control and Prevention, but
the disease is serious: About 36 percent of cases were fatal.

Dearing and her colleagues wanted a way to not just track
outbreaks, but to predict them. The research team set about
collecting two types of data. First, they trapped hundreds of
mice during six field expeditions over three years. Each mouse
was tagged and tested for the disease before being released.

When trapping first began, the researchers feared contracting
hantavirus by handling the trapped rodents. To protect
themselves, they initially donned biohazard suits that look like
spacesuits, earning the nickname "hantanauts." After medical
researchers learned that hantavirus isn't easily transmitted by
handling mice (people usually get it when cleaning out dusty,
enclosed spaces contaminated with mouse
feces ), the research team was able to ditch the suits.

Second, the team pulled data from MODIS, or the Moderate
Resolution Imaging Spectroradiometer, a sensor on NASA's Terra
satellite. The MODIS images of the field area in Juab County,
Utah, were analyzed to measure the green light reflected by
plants' leaves and the infrared light that plants absorb. More
green and less red meant more vegetation.

Disease-monitoring from space

The researchers expected the mouse population to surge after
vegetation peaked, but they didn't know how long it would take.
They tested correlations between vegetation and the number of
trapped and infected mice at about three-and-a-half months after
a vegetation peak, one year after, and one year and
three-and-a-half months after.

They found that the mouse population boomed one year after a
vegetation surge and then boomed again three-and-a-half months
after that. The proportion of hantavirus-infected mice trapped
didn't change, but the absolute number of infected mice went up
along with the population.

"You can think of it as a kind of air drop of food for the mice,"
study co-author Thomas Cova, a geography professor at the
University of Utah, said in a statement. "It's rained and
suddenly there's just so much food that they're rich. They get
fat, population density goes up, and about a year-and-a-half
later, population peaks."

Because the satellite vegetation images so clearly predict mouse
population booms, health officials could use the information to
pinpoint where
hantavirus outbreaks are most likely to occur.

"Although the focus of this work is hantavirus in deer mice, it
contributes to our broader understanding of how to monitor the
spread of infectious diseases from space, which in the long run
could save lives," Cova said.